The invention relates to powdered thickener preparations based on polyurethane, which can be incorporated particularly well into water-based paints and lacquers and into other aqueous systems, and to their use as rheological additives for thickening preferably aqueous systems.
Polyurethane-based thickeners for aqueous systems are described in numerous publications (see for example DE-A 1 444 243, DE-A 3 630 319, EP-A-0 031 777, EP-A-0 307 775, EP-A-0 495 373, U.S. Pat. Nos. 4,079,028, 4,155,892, 4,499,233 or 5,023,309).
A common feature of some thickeners from the prior art is the simultaneous presence of (i) hydrophilic segments in a quantity of at least 50 wt. %, (ii) hydrophobic segments in a quantity of no more than 10 wt. % and (iii) urethane groups. “Hydrophilic segments” here means, in particular, polyether chains with at least 5 links, the alkylene oxide units of which contain at least 60 mole % ethylene oxide units. “Hydrophobic segments” here means, in particular, hydrocarbon segments with at least 6 carbon atoms.
These polyurethane thickeners are suitable as auxiliary substances for adjusting rheological properties of aqueous systems such as automotive and industrial lacquers, stucco- and other paints, printing inks and textile dyes, pigment printing pastes, pharmaceutical and cosmetic preparations, plant protection formulations, filler dispersions and others.
Although the known polyurethane thickeners are widely used, they exhibit some disadvantages. Most of the available products are offered as liquid preparations, as a result of which the lacquers and/or paints in which they are applied are diluted. Particularly when a pre-diluted thickener is added, there is a negative effect on the solids content and other properties of the paint. In addition, the accurate metering of liquid thickener preparations, which may be diluted to concentrations <20%, is difficult in many production plants, or is possible only by complex technical means.
Another disadvantage of the liquid thickener formulations, especially at approx. 50% thickener concentration is the large space requirement, not only for the products as supplied but especially for the pre-diluted mixtures (generally 1:9). Additionally, the known polyurethane thickener formulations generally contain solvents and/or emulsifiers, which is disadvantageous for modern, low-VOC coatings and can also can cause risks to the environment when these are released.
Even the known powdered products consisting of 100% thickener are not ideal. They can often be incorporated into lacquers or paints only with difficulty and thus lead to lump formation in the lacquer mixtures. In addition, their thickening effect is often inadequate. The production of solid thickeners can also be difficult, since their ingredients (active substances) are usually waxy at room temperature so that free-flowing powders, having a long shelf life, cannot be produced.
It is an objective of the present invention to develop novel powdered thickeners based on polyurethane, which are powdered, free-flowing and have a long shelf life, can be readily incorporated and lead to lacquers and/or paints with good rheological properties.
This objective has been realized by polyurethane thickener mixed with a support that is solid at room temperature, in such a way that a free-flowing powder is obtained, which can be readily incorporated into paints and/or lacquers and other aqueous systems, imparting excellent rheological properties to them.